Assembly of iron-bound ovotransferrin amyloid fibrils

Fabrication of bovine serum albumin nanofibrils: Physicochemical characteristics, emulsifying and foaming activities

Bovine serum albumin nanofibrils (BSNs) were fabricated under thermal treatment (85 °C) at acidic condition (pH 2.0) and the incubation time on the structural, and physicochemical characteristics were probed. The formation and development of BSNs have been detected and confirmed by Thioflavin T (ThT) fluorescence and circular dichroism (CD) measurements. The structural alterations of bovine serum albumin (BSA) have also been investigated using intrinsic fluorescence and Congo red (CGR) UV-vis spectroscopy. Atomic force microscopy (AFM) outcomes displayed the morphologies of BSNs at varied time, with a diameter of about 3 nm and a contour length of about 200 nm at 24 h. The apparent viscosities of BSNs at three different pH were in the following order: pH 3.0 > pH 5.0 > pH 7.0. Emulsifying and foaming properties of BSA were pronouncedly enhanced through fibrillation, which was highly correlated with the interfacial properties and structural characteristics. Highest EAI 54.2 m2/g was attained at 48 h and no pronounced alterations were observed for EAI at 24 h and 48 h. Maximum value of FC was obtained at 48 h for BSA. This study will provide some useful information in understanding the formation of BSNs and broaden their application in food systems as functional food ingredients.

Specific ions effect on aggregation behaviors and structural changes of amyloid fibrils from rice glutelin

Metal ions have been considered as an important factor on fibrils assembly. Herein, a comprehensive analysis of specific ions effect on fibril formation and structural changes was investigated. The addition of ions (except Zn2+) accelerated the aggregation kinetics of rice glutelin fibrils (RGFs) from 0.93 to 1.28-2.19 h-1. In addition, the fibrillization rate followed the order of NH4+ > Li+ > Na+ > K+ > Cu2+ > Mg2+ > Ca2+ > Zn2+. The highest yield and length of fibrils were observed with Ca2+, probably due to the ionic bridging effect and hydrated capacity of Ca2+. However, Cu2+ reduced the fibrils yield, which was attributable to the fact that Cu2+ disrupted β-sheet structure and inhibited the transition of monomer to fibrils. The polymorphism of fibrils was observed with different salts, and the light metals presented a superior effect on fibrils formation than heavy metals. Overall, this work will provide a further information into how to tune the structure of RGFs using various ions.

Pretreatment with low-frequency magnetic fields can improve the functional properties of pea globulin amyloid-like fibrils

Plant protein fibrils have recently attracted considerable attention due to their superior mechanical and interfacial properties. The objective of this study was to evaluate the feasibility of low-frequency magnetic field (LF-MF) pretreatment in enhancing the conversion and functional characteristics of the amyloid-like fibrils derived from pea globulin (PG), which was considered a sustainable hypoallergenic protein. The results showed that LF-MF-treated PG (MPG) assembled into longer amyloid-like fibrils compared with native PG (NPG). The MPG presented similar gelling, emulsifying, and foaming properties to the NPG, while the fibril samples exhibited significantly improved functional properties. Moreover, the amyloid-like fibrils generated from the MPG (MPGF) showed large aspect ratios accompanied by superior solubility, molecular flexibility, emulsion stability, and gelling properties. The improved functional properties of the amyloid-like fibrils generated from the MPG can provide a promising outlook for expanding the applications of the PG in food, medicine and other fields.

Ovotransferrin Fibril-Gum Arabic Complexes as Stabilizers for Oleogel-in-Water Pickering Emulsions: Formation Mechanism, Physicochemical Properties, and Curcumin Delivery

This project aimed to explore the influence of the interaction between ovotransferrin fibrils (OTF) and gum arabic (GA) on the formation mechanism, physicochemical properties, and curcumin delivery of the oleogel-in-water Pickering emulsion. Cryo-scanning electron microscopy results showed that OTF-GA complexes effectively adsorbed on the oil-water interface, generating spatial hindrance to inhibit droplet coalescence. The texture analysis also proved that OTF-GA complexes endowed oleogel-in-water Pickering emulsion with preferable springiness (0.49 ± 0.03 mm), chewiness (0.43 ± 0.07 mJ), and adhesion (0.31 ± 0.01 mJ). By exploring the coalescence stability, droplet size, and rheological properties of OTF-GA complexes-stabilized oleogel-in-water Pickering emulsion (OGPE), the higher coagulation stability, larger average droplet size (46.22 ± 0.08 μm), and stronger gel strength were observed. The microrheological results also exhibited stronger attraction between the OGPE droplets, a more pronounced solid-like structure, and a slower speed of movement than OTF-stabilized oleogel-in-water Pickering emulsion (OPE). Meanwhile, OGPE significantly enhanced the extent of lipolysis, stability, and bioaccessibility of curcumin, suggesting that it possessed superior performance as a delivery system for bioactive substances. This project provided adequate theoretical references for protein-polysaccharide complexes-stabilized oleogel-in-water Pickering emulsion, and contributed to expanding the application of oleogel-in-water Pickering emulsion in the food industry.

Formation of pH-responsive hydrogel beads and their gel properties: Soybean protein nanofibers and sodium alginate

Hydrogel beads prepared from protein nanofibers are popular because of their safety, sleek appearance, and protection of biologically active substances. However, extreme external environmental variations, such as pH and temperature, can limit their practical application. To meet the application requirements of hydrogel beads in different environments, non-covalent mixtures of CaCl2 cross-linked soybean protein nanofibers (SNF) and sodium alginate (SA) were used to prepare hydrogel beads. In the present study, the hardness (782.48 g) and elasticity of hydrogel beads formed at SNF/SA = 7:3 and CaCl2 concentration of 0.1 mol/L were the maximum. Furthermore, the water content and pH swelling also reached a peak (98.68 %, 43.85 g/g) due to the best morphology and regular internal network structure. Meanwhile, the pH-responsive hydrogel beads with added anthocyanins were able to respond to the ambient pH under different temperatures and pH conditions and maintained color stability during 96 h of storage (ΔE < 5). In this experiment, a pH-responsive hydrogel bead based on soybean protein nanofiber (SNF) and sodium alginate (SA) was prepared by simple ionic crosslinking. It provides a theoretical and experimental basis for the future application of plant protein nanofibers as pH-responsive hydrogel materials.

The impact of different soluble endogenous proteins and their combinations with β-glucan on the in vitro digestibility, microstructure, and physicochemical properties of highland barley starch

The impacts of protein types and its interaction with β-glucan on the in vitro digestibility of highland barley starch were investigated through analyzing physicochemical and microstructural properties of highland barley flour (HBF) after sequentially removing water- (WP), salt- (SP), alcohol- (AP) and alkali-soluble (AlkP) proteins. Resistant starch (RS) increased significantly in HBF after removing WP and SP, and RS of HBF was lower than that of without β-glucan. After removing WP, SP and AP, swelling powers of HBF without β-glucan (9.33-9.77) were higher than those of HBF (12.09-15.95). Trends of peak viscosity and peak temperature (thermal degradation temperature) were similar as swelling power, and HBF without AP showed the highest peak temperature (310.33 °C). Removals of different proteins improved the crystalline structure and short-range order of starch. There was a blue shift in T2 values and an opposite change in free water proportion. The matrix on starch surface was mainly formed by AP and AlkP, which could be aggregated by β-glucan. But, the inhibitory effect of AP or AlkP was stronger than that of proteins combined with β-glucan. These results help in the development of starch-based foods with different digestive properties by combining different protein types with β-glucan.

Structure-property relationship of pea protein fibrils in stabilization of HIPEs and the encapsulation, protection, controlled release and oral delivery of carotenoids for alleviating intestinal inflammation

Increasing attentions are paid to high internal phase emulsions (HIPEs) due to their unique properties. In this study, pea protein-based fibrils were used as emulsifier to stabilize HIPEs. We demonstrated that the molecular assembly pathway and interfacial behavior of pea protein-based fibrils are affected by ionic strength. And the increased abundance of highly flexible worm-like nanofibrils facilitated their adsorption and packing on oil droplets, resulting in improved emulsion properties to stabilize the HIPEs with the internal phase volume fraction as high as 90%. Based on this, high loading content of carotenoids up to 0.05 wt% in the prepared HIPEs, protection of their stability against heating, UV and iron ions, and significantly increased bio-accessibilities of the carotenoids were realized. Animal studies using a mouse model of DSS-induced colitis revealed that carotenoid loaded HIPEs can alleviate the colon injury, by downregulating the expression of inflammatory cytokines, and promoting intestinal barrier function. This work will deepen the understanding of the formation of pea protein fibrils and provide a reference for the rational use of carotenoid loaded HIPEs in IBD management.

Formation of rice protein fibrils is highly sensitive to the different types of metal ions: Aggregation behavior and possible mechanisms

The effects of Ca2+, Cu2+, and Fe3+ on rice protein (RP) fibril formation were investigated in this study. Low Ca2+ concentration (≤150 mM) moderately unfolded the conformation of RP, promoting the exposure of hydrophobic sites and RP fibril assembly. Fibril formation was especially promoted with earlier addition of Ca2+. Cu2+ and Fe3+ inhibited RP fibril formation in a dose-dependent manner, and the inhibitory effect of Fe3+ was stronger due to higher affinity with RP. Additionally, the addition of Cu2+ and Fe3+ reduced α-helix and β-sheet contents of RP, respectively, hindering the formation of stacked β-sheet, the main internal structure of fibrils. These two ions also resulted in the formation of random aggregates within 15-50 nm, which further inhibited the conversion of proteins to fibrils. Moreover, Cu2+ and Fe3+ prevented the recruitment of nucleus into fibril-growth-sites, and formed fibrils were disrupted into fragments when these ions were added.

Formation, structure and functional characteristics of amyloid fibrils formed based on soy protein isolates

Food protein-derived amyloid fibrils possess great untapped potential applications in food and other biomaterials. The objective of this report was to investigate the formation mechanism, structure and functional characterization of soy protein amyloid fibrils (SPF) through hydrolysis and heating (pH 2.0, 85 °C, 0-24 h) of soy protein isolate (SPI). Fibrillation growth analysis indicated polypeptide hydrolysis upon hydrolytic heating, and the amyloid fibrils were basically formed 8 h later. The microstructure of SPF was monitored by transmission electron microscopy and scanning electron microscopy, exhibiting change from an irregular spherical structure to a coiled, intertwined thread-like polymer. The secondary structures of SPI all changed drastically during the fibrillation process was characterized by Fourier transform infrared spectroscopy, which the α-helical and β-turned content decreasing by 12.67 % and 5.07 %, respectively, and the content of ordered β-folded structures increasing with heating time, finally increasing to 53.61 % at 24 h. The fluorescence intensity of the endogenous fluorescence spectra decreased and the maximum emission wavelength was red-shifted, suggesting that the fibrillation unfolded the protein structure, hydrolyzed and self-assembled into amyloid fibrils aggregates obscuring the aromatic amino acid residues. The emulsification activity, emulsion stability and viscosity of SPF improved with the increase in protein fibrillation.

Precise control of aggregation morphology: Effective strategy to tune the properties of ovotransferrin particles

Different aggregation morphologies of ovotransferrin (OVT) aggregates were successfully obtained through precise control, and the effects on structural, physical, liquid-liquid and gas-liquid interfacial characteristics as well as mechanisms were explored for the first time. It was observed that the surface hydrophobicity of OVT fibrils was higher than OVT spheres due to the acid-heat treatment. The exploration of liquid-liquid interface behaviors indicated that OVT fibrils possessed higher adsorption capacity at the interface, revealing the higher surface activity at the oil-water interface. During adsorption process, fibrils exhibited higher diffusion rate, while spheres were easier to penetrate and rearrange at the interface. The interfacial film composed of fibrils possessed more elastic solid-like behaviors owing to the higher surface activity of individual fibrous aggregates and rapid fibril-fibril interactions. The analysis of gas-liquid interface characteristics presented that OVT spheres possessed lower interfacial tension and higher interfacial viscoelasticity, and showed significantly higher FC and FS values in comparation to fibrils. These findings will facilitate the reader's understanding of the relationship between protein aggregate structure and properties, and lay a foundation for broadening the application of OVT and even other proteins.

Biogenic engineered nanomaterials for enhancing bioavailability via developing nano-iron-fortified smart foods: advances, insight, and prospects of nanobionics in fortification of food

Iron deficiency is a significant cause of iron deficiency anemia (IDA). Treatment of IDA is challenging due to several challenges, including low target bioavailability, low palatability, poor pharmacokinetics, and extended therapeutic regimes. Nanotechnology holds the promise of revolutionizing the management and treatment of IDA. Smart biogenic engineered nanomaterials (BENMs) such as lipids, protein, carbohydrates, and complex nanomaterials have been the subject of extensive research and opened new avenues for people and the planet due to their enhanced physicochemical, rheological, optoelectronic, thermomechanical, biological, magnetic, and nutritional properties. Additionally, they show eco-sustainability, low biotoxicity, active targeting, enhanced permeation and retention, and stimuli-responsive characteristics. We examine the opportunities offered by emerging smart BENMs for the treatment of iron deficiency anemia by utilizing iron-fortified smart foods. We review the progress made so far and other future directions to maximize the impact of smart nanofortification on the global population. The toxicity effects are also discussed with commercialization challenges.

Nuclei-induced formation of amyloid fibrils in whey protein: Effects of enzyme hydrolysis on the ability of nuclei to induce fibril formation

Homogeneous and secondary nuclei (HN and SN) are aggregates formed at different stages of whey protein isolate (WPI) self-assembly. More fibrils can form when HN/SN are added as nuclei than when WPI self-assembles. We evaluated the effect of hydrolysis treatment on fibril-induction ability of nuclei derived from WPI, and investigated the relationship between induction ability and nuclear structure. Hydrolyzed SN-induced 9.47% more WPI fibrils than unhydrolyzed SN-induced. Infrared spectroscopy, X-ray diffraction analysis, and atomic force microscopy were used to examine the structural changes in hydrolyzed nuclei and the fibrils induced using these nuclei. We concluded that hydrolysis treatment led to a looser inter-β-sheet packaging in nuclei by increasing the inter-β-sheet distance. The inter-β-sheet distance of cross-β structure was a key determinant of fibril-induction ability of nuclei, which could be enhanced when inter-β-sheet structure was moderately loose. This research may provide a theoretical basis for the mechanism of nuclei-induced WPI fibrillation.

Fibrillation modification to improve the viscosity, emulsifying, and foaming properties of rice protein

Fibrillation of food proteins has attracted considerable attention as it can improve and broaden the functionality of proteins. In this study, we prepared three kinds of rice protein (RP) fibrils with different structural characteristics by the regulation of NaCl and explored the effect of protein structure on viscosity, emulsifying, and foaming properties. AFM results showed fibrils formed at 0 and 100 mM NaCl were mainly in the range of 50-150 nm and 150-250 nm, respectively. Fibrils formed at 200 mM NaCl were in the range of 50-500 nm and protein fibrils longer than 500 nm increased. There was no significant difference between their height and periodicity. Fibrils formed at 0 and 100 mM NaCl were more flexible and unordered than those formed at 200 mM NaCl. The viscosity consistency index K of native RP and fibrils formed at 0, 100, and 200 mM NaCl were determined. The K value of fibrils was higher than that of native RP. The emulsifying activity index, foam capacity and foam stability were enhanced by fibrillation, while longer fibrils exhibited lower emulsifying stability index, which may be because long fibrils resulted in difficulty of cover of emulsion droplets. In summary, our work provided a valuable reference for improving the functionality of rice protein and facilitated the development of protein-based foaming agents, thickeners, and emulsifiers.

Fibrillization kinetics and rheological properties of panda bean (Vigna umbellata (Thunb.) Ohwi et Ohashi) protein isolate at pH 2.0

Recently, research interests are growing regarding the formation and mechanisms of amyloid fibrils from plant proteins. This study investigated the fibrillization kinetics and rheological behaviors of panda bean protein isolate (PBPI) at pH 2.0 and 90 °C for various heating times (0-24 h). Results showed that PBPI formed two distinct classes of fibrils after heating for 10 h, including flexible fibril with a contour length of ∼751 nm, and rigid fibril with periodicity of ∼40 nm. The secondary structural changes during fibril formation were monitored by circular dichroism spectroscopy and indicated that β-sheet content increased first (0-12 h) and then decreased (>12 h), which coincided with similar changes in thioflavin T fluorescence. The gel electrophoresis revealed that the polypeptides of PBPI were progressively hydrolyzed upon heating, and the resulting short fragments were involved in fibril formation rather than PBPI monomer. PBPI-derived fibrils showed extremely high viscosity and storage modulus. A plausible molecular mechanism for PBPI fibrillation process was hypothesized, including protein unfolding, hydrolysis, assembly into matured fibrils, and dissociation of the fibrils. The findings provide useful information to manipulate the formation of legume proteins-based fibrils and will benefit future research to explore their potential applications.

Inhibiting ice recrystallization by amyloid protein fibrils

Ice recrystallization is harmful to the quality of frozen foods and the cryopreservation of cells and biological tissues, requiring biocompatible materials with ice recrystallization inhibition (IRI) activity. Emerging studies have associated IRI activity with amphiphilic structures. We propose amphiphilic amyloid protein fibrils (APFs) may be IRI-active. APFs were prepared from whey protein isolate (WPI) in water (W-APFs) and in trifluoroethanol (TFE-APFs). W-APFs and TFE-APFs were more IRI-active than WPI over a concentration range of 2.5-10.0 mg/mL. Both APFs showed stronger IRI activity at pH 3.0 than at pH 5.0, 7.0, and 10.0, which was ascribed to the effect of water dispersibility and fibril length. The reduced IRI activity of the two APFs with increasing NaCl content was caused by fibril aggregation. Ice binding by APFs was absent or very weak. Ordered water was observed for the two APFs, which might be essential for IRI activity. Our findings may lead to the use of APFs as novel ice recrystallization inhibitors.

Fibrous and Spherical Aggregates of Ovotransferrin as Stabilizers for Oleogel-Based Pickering Emulsions: Preparation, Characteristics and Curcumin Delivery

This study aimed to explore the effects and mechanisms of differently shaped aggregates of ovotransferrin (OVT) particles on oleogel-based Pickering emulsions (OPEs). Medium-chain triglyceride oil-based oleogels were constructed using beeswax, and their gel-sol melting temperatures were investigated. Atomic force microscopy confirmed that both OVT fibrils and OVT spheres were successfully prepared, and the three-phase contact angle measurements indicated that fibrous and spherical aggregates of OVT particles possessed great potential to stabilize the OPEs. Afterward, the oil-in-water OPEs were fabricated using oleogel as the oil phase and OVT fibrils/spheres as the emulsifiers. The results revealed that OPEs stabilized with OVT fibrils (FIB-OPEs) presented a higher degree of emulsification, smaller droplet size, better physical stability and stronger apparent viscosity compared with OPEs stabilized with OVT spheres (SPH-OPEs). The freeze–thaw stability test showed that the FIB-OPEs remained stable after three freeze–thaw cycles, while the SPH-OPEs could barely withstand one freeze–thaw cycle. An in vitro digestion study suggested that OVT fibrils conferred distinctly higher lipolysis (46.0%) and bioaccessibility (62.8%) of curcumin to OPEs.

Covalent modification of zein with polyphenols: A feasible strategy to improve antioxidant activity and solubility

Covalent modification of protein with polyphenols is an attractive research topic, since it is an effective way to improve the properties and broaden the applications of protein. However, the majority of prolamin-polyphenol reactions were carried out in alcohol aqueous solution, and this study aimed to investigate the covalent interaction of zein and polyphenols in water. Chlorogenic acid (CGA), gallic acid (GA), and caffeic acid (CA) were used as polyphenol models. The grafting ratio revealed that zein interacted more strongly with CGA and CA than with GA, which was probably due to the larger molecular weight of CGA and the hydroxycinnamic acid structure of CA. Afterward, the differences in structural and functional properties between control zein and zein-polyphenol complexes were compared. Covalent interaction with polyphenols induced great changes in the morphology and secondary structure of zein. Compared with control zein and non-covalent complexes, covalent zein-polyphenol complexes exhibited better solubility, antioxidant activity, and thermal stability. PRACTICAL APPLICATION: Covalent modification of zein with polyphenols in water is a simple and efficient method, which can ameliorate the antioxidant activity as well as the hydrophilicity of zein and improve its application value. The findings of this research carry important implications for using zein-polyphenol complexes as novel food additives, or to design more efficient delivery systems.

Iron delivery systems for controlled release of iron and enhancement of iron absorption and bioavailability

Iron deficiency is a global nutritional problem, and adding iron salts directly to food will have certain side effects on the human body. Therefore, there is growing interest in food-grade iron delivery systems. This review provides an overview of iron delivery systems, with emphasis on the controlled release of iron during gastrointestinal digestion, as well as the enhancement of iron absorption and bioavailability. Iron-bearing proteins are easily degraded by digestive enzymes and absorbed through receptor-mediated endocytosis. Instead, protein aggregates are slowly degraded in the stomach, which delays iron release and serves as a potential iron supplement. Amino acids, peptides and polysaccharides can bind iron through iron binding sites, but the formed compounds are prone to dissociation in the stomach. Moreover, peptides and polysaccharides can deliver iron by mediating the formation of ferric oxyhydroxide which is absorbed through endocytosis or bivalent transporter 1. In addition, liposomes are unstable during gastric digestion and iron is released in large quantities. Complexes formed by polysaccharides and proteins, and microcapsules formed by polysaccharides can delay the release of iron in the gastric environment and prolong iron release in the intestinal environment. This review is conducive to the development of iron functional ingredients and dietary supplements.

Formation, structural characteristics, foaming and emulsifying properties of rice glutelin fibrils

The rice glutelin fibrils (RGFs) were formed under heating at acidic condition, and the optimal condition was achieved at pH 2, 150 mM (ionic strength), 4% (protein concentration), 90 °C and 300 rpm (stirring speed) through the thioflavin T intensity. The atomic force microscopy images showed that the average contour length of RGFs increased from < 100 to 365 nm under the optimal fibrillation. The average particle size of rice glutelin (RG) decreased from 650 to 221 nm after initial heating time. Combining the degraded subunits, it suggested that RG was hydrolyzed to peptides, then these released peptides assembled into the ordered fibrils via intermolecular interactions, accompanying by the structural rearrangement. Additionally, the foaming and emulsifying properties were improved during fibrillation, which could be related to the interfacial properties and structure of RGFs. This work will deepen the understanding of the formation of RGFs and explore their potential application.

Hydrogels assembled from ovotransferrin fibrils and xanthan gum as dihydromyricetin delivery vehicles

Novel ovotransferrin fibril–xanthan gum hydrogels were assembled to deliver dihydromyricetin effectively.

Modulation of Formation, Physicochemical Properties, and Digestion of Ovotransferrin Nanofibrils with Covalent or Non-Covalent Bound Gallic Acid

The impact of covalent or non-covalent bound gallic acid (GA) on the formation, physicochemical properties, and digestion of ovotransferrin (OTF) nanofibrils was comprehensively studied. Thioflavin T fluorescence results revealed that bound GA could inhibit OTF nanofibrillation and that the fibril-inhibitory activity of bound GA was dose dependent. Covalent bound GA exerted stronger inhibition on OTF nanofibrillation than an equal amount of non-covalent bound GA. Atomic force microscopy revealed that covalent bound GA shortened OTF nanofibrils significantly, while non-covalent bound GA did not change the contour length of OTF fibrils remarkably. Bound GA altered diameter of OTF nanofibrils. Both covalent and non-covalent bound GA could alter the zeta potential, surface hydrophobicity, and rheological properties of OTF nanofibrils. Bound GA endowed OTF nanofibrils with a strong antioxidant activity. In vitro gastrointestinal digestion results showed that covalent bound GA elevated the fibril digestion rate better than non-covalent bound GA. Polyphenol binding provided a new approach to modulating the physicochemical properties of protein nanofibrils.